In recent times, an automobile, equipped with a power slide door or a hinged door that are operated to be opened/closed by use of electric power, hydraulic power or the like, has been in practical use. According to such automobile, a tilt angle of the automobile may be detected in order to adjust a level of the operational force, generated by the electric power, the hydraulic power or the like, used for the opening/closing operation of the door. The detection of the tilt angle is also useful for a power control at the time when the vehicle starts moving on a sloping road. One example of a sensor for detecting the tilt angle of the vehicle is disclosed in JP2002-318113A. A tilt sensor disclosed in JP2002-318113A includes a guide portion formed with a V-shaped groove in its cross section and a light shield body formed in a sphere shape and inserted into the guide portion. The tilt sensor in this configuration works to detect a degree of a sloping road (detect a tilt angle of a vehicle in a front-rear direction thereof) on the basis of a position of the light shield body detected by means of a photoelectric element.
Further, in order to improve a level of performance of a safety equipment such as a seatbelt, an air-bag or the like, an actuation of the safety equipment may be controlled in accordance with a weight of a passenger sitting on a vehicle seat to which the safety equipment is provided. For example, when a passenger sitting on the seat does not fasten the seat belt, the passenger is generally notified of not wearing the seat belt by an alarm or warning. The law in the United States states that, when an adult is sitting on a passenger seat, an air-bag must be deployed in the event of a vehicle collision or the like. On the other hand, the law also states that, when a passenger such as a baby or a child is placed in a child seat fixed on the passenger seat in a manner where the occupant of the child seat faces the seat back of the passenger seat, the air-bag must not be deployed because an impact caused by the deployed air-bag may cause damage to the occupant of the child seat in a car accident. A determination that the passenger sitting on the passenger seat is an adult, is executed on the basis of a value of a weight of an adult female whose weight is relatively light and height is relatively low. A determination that the passenger sitting on the passenger seat is a child, is executed on the basis of a suitable basis. Thus, in view of safety matter, it is important to determine a type of the passenger on the basis of a weight of the passenger.
One example of an apparatus for measuring the weight of the passenger, in other words measuring a level of a load applied to the supporting portion of the vehicle seat, is disclosed in JP3904913B describing a load detecting structure for a vehicle seat. The load detecting structure includes a load detecting means using four strain gauges provided at four positions, respectively, between lower rails attached to a vehicle seat and leg members attached to a vehicle floor, and the weight of the passenger is calculated by summing up the loads detected by the four strain gauges. Further, in order to determine whether or not a passenger is sitting on the vehicle seat or to determine whether a passenger sitting on the vehicle seat is an adult or a child, measuring an accurate load does not necessarily. Thus, there exists load detecting means provided at one of supporting portions of the vehicle seat in order to detect a partial load value of the load applied to the vehicle. The seat weight measuring apparatus disclosed in JP2001-150997A is configured by a sensor provided at one of three supporting portions, a front-right supporting portion, a front-left supporting portion and the rear-center supporting portions, of the vehicle seat. Specifically, the sensor is provided at the rear-center portion of the vehicle seat. In this configuration, the number of the load sensors may be reduced, thereby reducing costs of the parts and costs of assembling and wiring.
The apparatus disclosed in JP2001-150997A for detecting the partial load applied to the vehicle seat is preferable in view of the cost reduction, however, because the detected load value may vary in accordance with the tilt angle of the vehicle, the result determined by the apparatus disclosed in JP2001-150997A is less accurate compared to the apparatus disclosed in JP3904913B in which a total load applied to the vehicle seat is detected. For example, because the load sensor disclosed in JP2001-150997A is provided at the rear of the seat, when the vehicle is moving down on the sloped road, the load sensor is assigned to detect a small ratio of the load placed on the seat, compared to a situation where the vehicle is driving on a flat road. Thus, the load sensor may underestimate the load value applied to the vehicle seat. In order to increase a level of the determination accuracy, a tilt sensor for detecting a tilt angle of the vehicle may be additionally provided, however, the cost of the apparatus is increased by a cost for the tilt sensor, thereby offsetting the cost reduction achieved by reducing the number of the load sensors. The detected tilt angle may be used for correcting the load applied to the vehicle seat.
A need thus exists for a vehicle tilt detecting apparatus having a seat load detecting apparatus, which is not susceptible to the drawback mentioned above.